VP - C25 vs C12 or C14
 

In going from C12 or C14 to C25, how much larger jet is usally required in a holley 750 or similar sized carb. It seems about 2 sizes may be in the range, any throughs or comments appreciated. Thanks Bob

Re: VP - C25 vs C12 or C14
 

I found 2 jet sizes worked on the dyno going from 14 to 25.

Re: VP - C25 vs C12 or C14
 

When changing fuels, the general rule of thumb is to change one jet size for every .10 change in specific gravity ( Fuel Density).
For instance,
switching from a fuel SG of .720 to a fuel of .725 SG wouldn't require a change in jetting.
switching from a fuel SG of .720 to a fuel of .730 would require a change of 1 size in jetting.
And switching to oxygenated fuels will usually require up to four jet sizes higher to start.
Start out easy and let the plugs ( read all of them, not just a couple ) be your guide for further changes.

Re: VP - C25 vs C12 or C14
 

I tested C25 against C12.
Found it gave me 1 mph but lost .05 overall. Lost .10 in the sixty, .15 in the eight, but picked up .10 in the second half of the track.
This was just make 3 runs, change fuel, make 3 runs, back to original fuel make 3 runs.
I believe the C25 would be beneficial if I can do some tuning. But 9 runs in a day was enough. Later I might put the C25 back in and do some tuning. If I can get it to leave like the C12 it will be overall quicker. But so damn expensive.

Re: VP - C25 vs C12 or C14
 

Bob give me a call or shoot me an e-mail and I will talk to you about C25. Are you trying to switch to C25 for your Fairlane?

Re: VP - C25 vs C12 or C14
 

Did anyone's timing change with C-25?

Re: VP - C25 vs C12 or C14
 

Run one - two degrees less timing.

Re: VP - C25 vs C12 or C14
 

Thanks. I've seen as much as 4, and as little as 1 degree difference. Just wondering if I was seeing right.